Learning in your sleep can really stink

Learned associations between odors and sound persist to the next day.

The owls may be telling you something. And, if new results are to be believed, you may learn something from them.

The Sleep of Reason Produces Monsters, by Francisco Goya

Sleep appears to play a key role in helping the brain consolidate the memories it forms during the day. While past research has indicated that you can't form new memories during sleep, a new study has found that the brain can establish new associations while sleeping. There's a catch, though: its capacity may be limited to certain types of memories—in this case, ones associated with the sense of smell.

Plenty of experiments have looked at the role of sleep in consolidating memories. Rats, for example, seem to replay some of the travels they make during the day while asleep. The process appears to help solidify the memories, making them more accessible for future use. In rodents (and, in some limited cases, humans), it has been possible to perform some limited forms of conditioning while they're asleep. But forming more complex, long-term memories, like word associations, has generally failed. People clearly listen in their sleep, but they didn't seem to fully process what they were hearing.

In the new work, the authors decided (at least initially) to test whether associations that were established during sleep could be remembered within the same sleep session. Since you can't test for things like the ability to recall a word association while asleep, they focused on two sensory systems, hearing and smell, that we know are active while a person is asleep. And they established a simple measure of recall: even when asleep, people react positively to pleasant aromas, and will draw deeper breaths in response to them.

Believe it or not, the first step was actually to make sure that they had a reasonable knowledge of what constitutes a pleasant smell. "Deodorant and shampoo were significantly more pleasant than rotten fish and carrion," they determined after inviting subjects to breathe deeply. "In other words, we had achieved the intended psychophysical framework." With a measure of unpleasantness established, they next tracked sleepers' responses to pleasant and unpleasant odors, and detected a small but statistically significant difference between the two: a nice smell induced people to sniff longer, even when asleep.

(My guess is that the effect is small enough that, at least when measured by volume of the air sniffed, it would require a huge population to tell the difference between a nice aroma and a neutral one. Which explains why the authors measured the difference between two extremes.)

To try to form an association, the authors started playing simple tones as they exposed sleepers to pleasant or unpleasant smells. (People who showed signs of being woken by the tone itself were excluded from further analyses.) After a few training sessions, they started playing the tone without any odorant. Even though nothing was in the air, people still breathed more deeply when they heard a tone that had been paired with a pleasant odor earlier in the same sleep session.

The real surprise was that, even after they woke up, the association remained: playing the tone had people sniffing more intently if it had been associated with a pleasant aroma.

The researchers also compared the impact of the stage of sleep, and found something a bit odd. Once learned, an association was equally strong in both REM and non-REM sleep. But when it was learned it had a curious effect: associations learned during REM sleep were stronger when a person was still asleep, but associations learned during non-REM sleep were stronger once the subject woke up.

The authors themselves aren't totally confident in this pattern, because the numbers here got rather small—as noted above, testing stopped whenever a subject showed an indication that the tone was waking them up, and most people go through periods of disturbed sleep over the course of a night. As a result, lots of people were dropped from the analysis before they had the chance to wake up normally and undergo further tests. Another limit the researchers faced is the fact that playing the tone without an aroma (which is needed to test the association) will weaken the memory, so you can't test a subject too many times before destroying the effect you're testing for.

Nevertheless, the test subjects indicated they had no memory of the training that took place while they were asleep. And, better yet, people who were exposed to pleasant smells tended to stay in a sound sleep, even as various tones were played in their vicinity. The authors wrap up by suggesting that these techniques could not only help people sleep better, but they could also help them make better use of sleep. Since most of us spend a third of our lives asleep, that could prove helpful.

16 Reader Comments

The researchers might have discovered another measure for IQ. The smart ones woke up and got out of there! By any measure, being compared to a rat is very unappealing. Hearing un-natural noises while sleeping ought to wake up any reasonably intelligent human.

From the list of authors, it looks like none of my taxes paid for it. Good. This ranks up there with measuring bovine methane.

The researchers might have discovered another measure for IQ. The smart ones woke up and got out of there! By any measure, being compared to a rat is very unappealing. Hearing un-natural noises while sleeping ought to wake up any reasonably intelligent human.

Not really; rats make good stand-ins for humans in a lot of testing. Chemical, metabolic, even neurological. They're also cheap and, unlike monkeys, very few people give a shit if you infect a rat with super-ebola.

As for the sounds, intelligence has nothing to do with it. Some people are just deeper sleepers than others. Take myself; I've slept through tornadoes, and once while under about 3 inches of water (after I went to sleep), but a human voice will wake me up every time, unless I'm just exhausted.

And it's a useful thing to learn about. If they'd been able to determine, for example, that word-associations could be made to hold, that could have potentially huge effects on the educational system. For example, it could have opened a door to moving rote memorization from class hours to sleep hours.

Quote:

From the list of authors, it looks like none of my taxes paid for it. Good. This ranks up there with measuring bovine methane.

Which is actually a useful thing to know, when you have high densities of cattle.

The researchers might have discovered another measure for IQ. The smart ones woke up and got out of there! By any measure, being compared to a rat is very unappealing. Hearing un-natural noises while sleeping ought to wake up any reasonably intelligent human.

From the list of authors, it looks like none of my taxes paid for it. Good. This ranks up there with measuring bovine methane.

If your post is trolling, then I wish to congratulate you. If not, then I think we have a wonderful example of the Dunning-Kruger effect.

The researchers might have discovered another measure for IQ. The smart ones woke up and got out of there! By any measure, being compared to a rat is very unappealing. Hearing un-natural noises while sleeping ought to wake up any reasonably intelligent human.

From the list of authors, it looks like none of my taxes paid for it. Good. This ranks up there with measuring bovine methane.

If your post is trolling, then I wish to congratulate you. If not, then I think we have a wonderful example of the Dunning-Kruger effect.

Awesome.

Also, this is actually a really interesting and useful study - The general body of knowledge on the mechanics and biological systems involved in sleep is small, but growing steadily. Any research that yields fruitful results is good research!

Now, can I be involved in sleep research? I have a hypothesis that viscoelastic foam sleep surfaces have an effect on REM sleep patterns and I need funding to test it out. I'm willing to be the first guinea pig... For science, y'know.

This experiment was one sided. It only tested on the city people. How about giving a test on people living in the farms all their lives and who got used to the awful smell of the dongs and cattle that no way any of the city people could stand it? The testing result may be the opposite. Bad smell leave the country people sound asleep and only waken by Chennel 5, the opposite of the city guys?

And if you fart right next to this country guy... It might actually help him getting a deeper sleep..

it has been possible to perform some limited forms of conditioning while they're asleep

In which case, here we have another study demonstrating "some limited forms of conditioning" (i.e. "classical" or "Pavlovian" conditioning). So how does this study differ from the others? Just because of the involvement of smell? Sounds like a good study (we actually don't know very much about memory formation OR sleep, and there are clear practical benefits to getting a better understanding of both), but it is a shame that the present article doesn't really give it any context. Non-experts need that context, or else they tend to walk away completely misunderstanding what the study was actually about (case in point: xwindowsjunkie's ignorant comments above). Speaking of which:

xwindowsjunkie wrote:

...it looks like none of my taxes paid for it. Good.

Yeah, 'cos what possible practical applications could there be for getting a better understanding of memory formation. It's not like people in the real world ever have to actually learn or remember anything. Figuring this stuff out, so that we can help people with learning and memory impairments, or just help the rest of us learn and remember more easily and reliably, seems like a total waste of money to me too.

Edit:

composer777 wrote:

xwindowsjunkie wrote:

(snip)

If your post is trolling, then I wish to congratulate you. If not, then I think we have a wonderful example of the Dunning-Kruger effect.

-Sadly, you will find that you run into an awful catch-22 situation whenever you attempt to point this out to one of the Dunning-Kruger effect's many victims.